The present invention relates to a digital video communication system.
With current digital video communication systems, a video signal source such as television camera is synchronized with a clock rate determined independently from the transmission rate of the system. Therefore the quantization sampling rate at which the video signal from the camera is digitized differs from the transmission sampling rate at which it is transmitted to a receiver station. If the receiver station communicates with multiple transmitter stations using different sampling frequencies, the video signals received from these sources must be synchronized with each other in order to allow several video programs to be processed with a single clock rate and to be cut and pasted onto a single screen. One approach is to use a frame synchronizer to eliminate the differences in clock rate. According to another prior art technique, the quantization sampling rate information is transmitted with a video signal encoded by a predictive encoder to a receiver station. The latter is provided with a clock recovery circuit with which the original sampling clock rate is recovered for dequantizing the digital video signal. A further approach as described in Japanese Patent 61-30456 involves the detection of the ratio between the quantization and transmission sampling rates. The detected ratio is multiplexed with a digitized signal and transmitted to a receiver station.
Any of the foregoing prior art approaches adds to the complexity and the total cost of the system. In addition, the use of the frame synchronizer, in particular, causes an out-of-sync condition with a received signal when channel switching occurs.